Mass spectrometric analysis of amino acid/di-peptide modified gemini surfactants used as gene delivery agents: Establishment of a universal mass spectrometric fingerprint

Abstract

Lipid based gemini surfactant nanoparticles have been extensively studied as non-viral vectors for gene therapy. Novel amino acid substituted gemini surfactants have been recently developed with a molecular structure consisting of two positively charged quaternary ammonium head groups, symmetrical saturated dodecyl tails, and a spacer region containing a secondary amine group. Various amino acids were attached to the amine functional group. The purpose of this work was to confirm the molecular structure of six novel amino acid substituted gemini surfactants and to establish a universal fragmentation (MS/MS) pattern of the tested compounds (i.e., fingerprint). This was accomplished by using a hybrid quadrupole orthogonal time-of-flight mass spectrometer (QqToF-MS) and a triple quadrupole linear ion trap mass spectrometer (QqQ-LIT MS) equipped with electrospray ionization (ESI) source. The single stage QqToF-MS data obtained in the positive ion mode verified the molecular composition of all tested gemini surfactants. Tandem mass spectrometric (MS/MS) analysis showed common fragmentation behaviour among all tested compounds, allowing for the establishment of a universal fragmentation pattern. The fragmentation pathway was confirmed by MS/MS/MS experiments utilizing a Q-Trap™ 4000 LC/MS/MS system. Unique product ions, originating from the loss of one or both head groups along with the attached tail region(s), confirmed the chemical structure of the tested compounds. The established MS/MS fingerprint will be used for qualitative purposes as well as the development of future multiple reaction monitoring (MRM) HPLC–MS/MS quantification methods.